And the answer is . . .

24. 

Remember you're trying to divide 12 poker chips into groups of 1/2 chip. Think of $12, instead if you had trouble with this. If there's only half a dollar per pile (say 5 dimes) it's going to take a LOT of piles to get the whole $12. It takes two piles just to get a dollar. It kind of makes sense that you need to multiply the 12 dollars times two stacks for every dollar.

So what's 12 / (1/4)?